1. Field of the Invention
The present invention relates to a structure of an exhaust system for a vehicle, and more particularly, to a structure of an exhaust system for a cylinder deactivation (CDA) engine, in which a main muffler is divided into four spaces by three baffles, and a first connecting pipe and a second connecting pipe which connect a second space and a third space, a first valve which is coupled to a passage of the first connecting pipe, and a second valve which is coupled to a passage of the second connecting pipe are provided, thereby reducing noise in the exhaust system with maximum efficiency in accordance with characteristics of an engine.
2. Description of Related Art
Recently, in respect to increased concerns about the environment, major issues such as an environmental problem with excessive emission of exhaust gas of a vehicle and consumers preferring a high efficiency vehicle because of an increase in cost of crude oil have become the focus.
Therefore, various technologies are being developed in order to improve fuel efficiency of a vehicle, and increase output of an engine.
For example, a variable induction system (VIS) which changes a length or a cross-sectional area of an intake manifold in accordance with air intake resistance that is varied depending on a rotational region of an engine, a variable valve timing (VVT) which adjusts an opening timing and an opening degree of a valve depending on a rotational region of an engine, a variable valve lift (VVL) which adjusts a lifting height of a valve, and a cylinder deactivation (CDA) which switches some cylinders in an engine to a non-operational state or a full operational state in accordance with a traveling state in order to improve fuel efficiency have been developed and used.
Among the aforementioned technologies, the CDA engine refers to an engine that deactivates some of the cylinders when braking the vehicle or when the vehicle travels at a constant speed, and fuel supply and operations of intake/exhaust valves are stopped at the deactivated cylinder side.
Because maximum output of the engine of the vehicle is required only when the vehicle accelerates or travels up a slope, fuel consumption may be reduced by not selectively igniting fuel in the cylinder in a case in which the vehicle may be operated by merely using partial output of the engine.
For example, in the case of the vehicle in which a four-cylinder engine is mounted, because there is no reason to operate all of the cylinders to generate power when braking the vehicle in a traveling state, or when the vehicle is in a low idle condition or a low load condition, two cylinders are deactivated, and power is generated only by the remaining two cylinders.
However, the CDA engine has advantages in that fuel consumption is low and fuel efficiency is high in comparison with a typical engine, but has problems in that because fuel in some of the cylinders is not ignited, the main component of engine noise is changed and low frequency noise is increased.
In order to solve the aforementioned problems, in a structure of an exhaust system for a CDA engine in the related art, as illustrated in FIG. 1, an additional muffler 2 is mounted in an exhaust pipe 4, which connects a sub muffler 1 and a main muffler 3, so that the entire exhaust pipe 4 is divided into several segments, thereby reducing noise.
That is, in the CDA mode in which only two cylinders of the four-cylinder engine are operated, a half order low frequency noise component (a noise component that corresponds to C1, C3, and the like among main components of engine noise), which is hardly generated in a general mode, is additionally generated, and combined with a low frequency resonance mode in the existing exhaust pipe, and as a result, there is a problem in that noise characteristics of the vehicle deteriorates.
Therefore, as illustrated in FIG. 2, the additional muffler 2 is mounted at peak points of a second resonance mode of the exhaust system and a fourth resonance mode of the exhaust system so as to reduce a resonance mode of the exhaust system.
However, in the case of the structure of the exhaust system for a CDA engine in the related art in which a separate additional muffler is mounted, there are still problems in that spaces for other components (a fuel tank, a rear suspension, an interior space, and the like) need to be decreased in order to mount the additional muffler between the sub muffler and the main muffler, and a weight of the vehicle is excessively increased because of the additional muffler.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.